Paspalum prodigiosum Sánchez-Ken, 2021

Sánchez-Ken, J. Gabriel, 2021, A new species of Paspalum (Paspaleae, Panicoideae, Poaceae) from Ario de Rosales, México, with partially homogenized synflorescences, Phytotaxa 498 (1), pp. 12-24 : 13-20

Paspalum prodigiosum Sánchez-Ken , sp. nov. ( Figure 1–5 )

Type:— MEXICO. Michoacán, Mpio. Ario de Rosales: Hacienda La Salvia , E de Los Tumines, 1,623 m, 19° 09’ 19” N, 101° 42ˈ 46” W, 12 March 2019, J. G . Sánchez-Ken , C. A . Cultid M. & A . Martínez J . 995 (holotype IEB!, isotypes EBUM!, MEXU!) .

Plants perennial, 55–90 cm tall, erect, with a knotty base, tufted, branched mainly below, sometimes branching above the base; internodes green, glabrous; nodes exposed, brown, lower ones pilose, upper ones becoming glabrous. Lower leaf sheaths longer than the internodes, overlapping, hirsute, margins glabrous to sparsely short pilose, the upper ones shorter than the internodes, glabrous, slightly keeled distally; ligules 0.6–1.1 mm long, membranous, glabrous, brownish; collar hirsute; leaf blades linear-lanceolate, (10–)20–28 × 0.4–0.9(–1.2) cm, the uppermost reduced in size, flat, base narrowed, sparsely hirsute on both surfaces, hairs ca. 1 mm long, throat long pilose, hairs ca. 5 mm long, margins scabrous, papillose-hirsute, apex acuminate. Synflorescences 9–17 cm long, terminal, pyramidal to slightly ovate; peduncles 14–22 cm long, glabrous; axis glabrous; primary branches 11–16(–24), 1–9.5 cm long, distributed along the main axis, proximal branches longer than the upper ones, usually with long isolated hairs at the base of the rachis; pulvini dark-brown, with a tuft of long hairs; primary branches partially homogenized, i.e. with 0.4–3 cm long secondary and/or tertiary branches at the base; rachis 0.3–0.6 mm wide, narrowly winged to triquetrous, terminating into a spikelet; spikelets mostly paired along the branches, rarely solitary, loosely arrange in 4 irregular series, pedicels unequal, 0.4–1.4 mm long, glabrous. Spikelets 1.6–1.7 × 1–1.1(–1.2) mm, elliptic to slightly obovate, plane-convex to slightly concave-convex, greenish to purple tinged, apex rounded to slightly acute, usually 2-flowered, rarely 3 with the two uppermost florets fertile and similar; first glume absent; second glume 0.1–0.2 mm shorter than the spikelet, papery, shortly papillose-hirtellous, hairs sometimes scattered, 3–4-veined, veins nearly joining at the apex; lower floret sterile, lower lemma as long as the spikelet (but shorter when the spikelet is 3-flowered), papery, glabrescent to sparsely papillose-hirtellous, 3–4-veined, veins joining at the apex; lower palea absent; upper floret fertile (rarely a third fertile floret present, fertile); upper lemma equal to slightly shorter than the spikelet (the uppermost slightly smaller than the lower one when spikelet is 3-flowered), cartilaginous, pale, minutely papillose, with minute appressed microhairs sparsely distributed; upper palea nearly as long as the upper lemma, sometimes slightly concave, minutely papillose, with few scattered appressed microhairs, slightly enclosed by the upper lemma margins; lodicules 0.25–0.3 mm long; stamens 3, anthers 0.8–0.9(–1) mm long, yellow to purple; stigmas purple. Caryopses 1–1.1 mm in diameter, slightly oblong to ovate, plane-convex, embryo ca. 0.4 mm long, up to third as long as the caryopsis, hilum ca. 0.43 mm long, oblong, a third to one fourth as long as the caryopsis.

Etymology: —The specific epithet, prodigiosum , is derived from the Latin word prodiguosa = strange or prodigious ( Clifford & Bostock 2007). It refers to the rare presence of 3-flowered spikelets, the upper two fertile and similar, and the lower one similar to the second glume.

Distribution and Habitat: —The new species is endemic to Mexico, occurring at the center of Michoacán. It was found growing among raspberry crops surrounded by a perturbed tropical deciduous forest at 1,621 –1,623 m ( Fig. 5 ). The only known population of Paspalum prodigiosum covers the whole area (approx. 1 km 2) where the raspberry is cultivated in Hacienda La Salvia. Most of the plants grow near the irrigation system, which suggests that the species is hygrophilous and probably was competing for water against the raspberry plants. The species might be threatened by weeding.

Phenology:— Flowering between March–April.

Additional Specimens Examined:— MEXICO. Michoacán: municipality Ario de Rosales, Hacienda La Salvia , E de Los Tumines, 1,621 m, 19°09’17”N, 101°42’50”W, 01 April 2019, J. G . Sánchez-Ken , C. A . Cultid M . & Antonio Martínez J . 1002 (EBUM, IEB, MEXU).

Photosynthetic Pathway and Leaf-Blade Micromorphology: — Photosynthetic pathway. Kranz anatomy or C 4 pathway was confirmed by the presence of chloroplasts in a single bundle sheath or mestome sheath, as well as by the irregularly radiated mesophyll composed of 2–3 cells between vascular bundles ( Fig. 2A ). The subtype is NADP- ME M.S., where the chloroplasts are within the mestome or inner bundle sheath ( Sage 2003). Primary, secondary, and tertiary vascular bundles are present ( Fig. 2A ). Large bulliform cells are also present, with large similar cells or parenchyma cells below towards the midvein ( Fig. 2A ).

Leaf blade Adaxial Epidermis. The adaxial epidermis of the leaf-blade presents cells of different size and shape in the costal and intercostal zones ( Fig. 2B ). The former is composed of single lines of long cells, which are up to twice as long as those of the intercostal zone, although some may be shorter, with walls nearly smooth. No other types of cells were found in the costal zones. The intercostal zone is composed of rectangular long cells with slightly undulated walls; bicellular microhairs with the apical cell slightly longer than the basal cell, distributed on the margins of the intercostal zone and sparsely in the middle; unicellular macrohairs with a swollen base, less frequent than microhairs, in the middle of the intercostal zone; prickles globose, scattered; single short cells very scattered between long cells around the middle of the intercostal zone; and, stomata forming parallel lines toward the costal zone, with subsidiary cells slightly triangular in shape ( Fig. 2B ).

Leaf blade abaxial epidermis. The abaxial epidermis differs from the adaxial epidermis ( Fig. 2C ). The costal zone is wider than the intercostal zone with 4–5 lines of long cells, which are longer than those of the intercostal zone, with moderately undulated walls; silica bodies irregular dumb-bell shaped; short-cells nearly similar to silica bodies; prickles globose, more abundant than in the adaxial surface; bicellular microhairs similar to those of the adaxial surface, less frequent; and, stomata scattered equal to those of the adaxial surface ( Fig. 2C ). The intercostal zone presents long-cells nearly square to rectangular, with slightly undulated walls; short-cells rectangular, tall and narrow, scattered; bicellular microhairs very scattered towards the middle; unicellular macrohairs abundant, with a swollen base ( Fig. 2C ).

Anatomy of the leaf blades of P. prodigiosum and P. paniculatum in cross section ( Fig. 2A,D ) was very similar, although the latter seems to have a slightly thinner leaf blade. The adaxial epidermis of P. prodigiosum ( Fig. 2B ) showed macrohairs, numerous stomata, elongated intercostal long cells, elongated and narrow costal long cells with smooth walls, and scattered rounded prickles, whereas in P. paniculatum ( Fig. 2E ) macrohairs were observed only at the edges of the leaf-blade, there was only a few stomata, the intercostal long cells were more squarish, the costal long cells were elongated, both long cells had lobulated walls, and there were prickles of two shapes, rounded in the intercostal zones, and elongated in the costal zones. The abaxial epidermis of both species ( Fig. 2C,F ) were similar, however, in P. prodigiosum there were macrohairs, and the long cells of both costal and intercostal zones were slightly larger than in P. paniculatum .

Caryopses and Starch Grains:— According to Tateoka (1962), Paspalum has starch grains Type 2, simple, with hexagonal, pentagonal, and rarely rectangular shape, not variable in size, although those toward the center of the endosperm seem a little smaller. Also, there are some very small bodies (1–2 µm) that do not stain, which probably are protein bodies and globulins, similar to those of maize and other andropogonean genera ( Coleman et al. 1997, Sabeli & Larkins 2009).

In Paspalum prodigiosum , caryopses are slightly oblong to ovate, ca. 1.1 mm in diameter, with an embryo ca. 0.4 mm long, and the hilum is oblong and ca. 0.43 mm long ( Fig. 3A ). The endosperm consists of simple starch grains and protein bodies (prolamins and/or globulins, Fig. 3B ). Starch grains are nearly circular, angular, squarish, pentagonal to somewhat irregular shaped, (4–)5–10(–11) µm in diameter ( Fig. 3B ). The majority of the grains are 5–7 µm in diameter and the heterogeneity in size is conspicuous ( Fig. 3B ).

In Paspalum paniculatum , a putative closely related species, the caryopses are nearly circular to slightly oblong, 0.7–0.9 mm in diameter, with an embryo ca. 0.38 mm long, and the hilum slightly oblong and ca. 0.2 mm long ( Fig. 3C ). The starch grains are circular, angular, squarish to hexagonal, (4–)6–10(–11) µm in diameter. The majority of the grains are 6–8 µm in diameter and the variation in size is not pronounced ( Fig. 3D ).

In Paspalum squamulatum , the caryopses are ovate to circular, 1.2–1.3 mm in diameter, with an embryo ca. 0.45 mm long, and the hilum oblong ca. 0.45 mm long ( Fig. 3E ). The starch grains are circular with few angular shapes (squarish to hexagonal), (3–)5–6(–9) µm in diameter ( Fig. 3F ). The majority of the grains are 5–6 µm and the variation in size is not pronounced ( Fig. 3F ).

The sizes of the starch grains of the three species are within the range stated by other authors ( Buleón et al. 1998).

Related Species: —Based on the size and shape of the spikelets and the numerous primary branches, Paspalum prodigiosum is here putatively assigned to the informal group Paniculata.In this group, the new species is morphologically more similar to P. paniculatum , but most of the vegetative characters of these species overlap ( Table 1), and so they cannot be considered diagnostic. The leaf blade base in P. paniculatum is usually subcordate to cordate, however, there are some specimens that have narrowed bases as in P. prodigiosum ( Fig. 4A,D ). More evident differences are found in the length of the spikelets, anthers, caryopses, and hilum, which are shorter in P. paniculatum than in the new species ( Table 1).

Regarding the presence of 3-flowered spikelets, only two or three were found in one specimen of P. paniculatum (terminal spikelet, Fig. 4B ), whereas in P. prodigiosum more than three 3-flowered spikelets were observed ( Fig. 4G ). It suggests that it is common feature in P. prodigiosum , and a rare feature in P. paniculatum . These spikelets look like a regular two-flowered spikelet with glumes, however, the lemma of the lower sterile floret cannot be considered as a glume because of its position and vein number ( Fig. 4C,H ). It resembles the second glume in texture and vein number ( Fig. 4C,H ) as in all species of the genus reviewed by the author. Furthermore, the upper two florets are hardened and pale, which are also the usual condition of the fertile florets in Paspalum ( Clayton & Renvoize 1986) .

Synflorescences:— The synflorescences of Paspalum prodigiosum are very similar to those of P. paniculatum , being composed of a main axis, and lateral primary branches that become shorter toward the apex, all of them terminating in a spikelet ( Fig. 1A ). However, almost all primary branches of P. prodigiosum have short secondary, tertiary or even quaternary branchings toward the base (i.e. primary branches are partially homogenized) ( Figs. 1A , 4F ).

After a survey of taxonomic works on Paspalum , only a few species with primary branches exhibiting other orders of branching were found ( Table 2), especially from the Quadrifaria informal group ( Chase 1929, Rua 1996, Morrone & Zuloaga 2005). Rua (1996) studied the synflorescences of the Quadrifaria informal group, including species from other informal groups like Virgata, Eriantha, and Corcovadensia, and suggested that the presence of higher orders of branching beyond the primary ones, an unusual attribute in the genus, was the most plesiomorphic form in the genus. More recently, in a molecular phylogeny of the genus, the relationships within Paspalum were not fully resolved, however, the basal groups recovered in the analyses have primary branches without further branchings ( Scataglini et al. 2014). Thus, the hypothesis raised by Rua (1996) should be rejected and the branching pattern found in the informal groups Coryphaea, Paniculata, Quadrifaria , and Virgata (plus an ungrouped species) ( Table 2) seems to be a novelty that arose during the evolution of the genus.

Figures

FIGURE 1. Paspalum prodigiosum Sánchez-Ken. A. Habit. B. Ligular area, adaxial view. C. Segment of a primary branch showing a 3-flowered spikelet (arrow). D. Spikelet, second glume dorsal view. E. Spikelet, sterile lemma ventral view. F. Fertile floret, fertile lemma view. G. Fertile floret, fertile palea view. H. Caryopsis, embryo view. I. Caryopsis, hilum view. Drawn from Sánchez-Ken et al. 995 (IEB).

FIGURE 2. Leaf anatomy of Paspalum prodigiosum Sánchez-Ken (A–B) and P.paniculatum L. (D–F). A and D. Leaf blade cross section. B and E. Leaf-blade paradermical section, abaxial surface. C and F. Leaf-blade paradermical section, adaxial surface. ab ep = abaxial epidermis, ad ep = adaxial epidermis, b c = bulliform cells, bs = bundle sheath, c z = costal zone, i z = intercostal zone, l c = long cell, m = mesophyll or chlorenchyma tissue, mah = macrohair base, mb = macrohair base, mih = microhair, p = prickles, ph = phloem, s = sclerenchyma, s c = short cells, si b = silica bodies, s c = short cells, st = stomate, vb = vascular bundle, x = xylem.

FIGURE 3. Caryopses in dorsal (left) and ventral (right) views, and stained cross-sections showing the starch grains. A–B. Paspalum prodigiosum Sánchez-Ken. C–D. Paspalum paniculatum L. E–F. Paspalum squamulatum E. Fourn.

FIGURE 4. Stereomicroscope images of vegetative and reproductive characters of Paspalum paniculatum L. (A–C) and P. prodigiosum Sánchez-Ken (D–H). A. and D. Ligular area, adaxial view (pseudoligule: left arrow; ligule: right arrow). B. Apex of a primary branch showing an apical 3-flowered spikelet. C. Spikelets (left two: 2-flowered; right: 3-flowered) and H. Spikelets (first: 3-flowered; right two: 2-flowered). E. Segment of a primary branch, proximal region showing secondary and tertiary branches (arrows). F. Segment of a primary branch, proximal region showing a short secondary branch with three spikelets (arrow). G. Segment of a primary branch, proximal region showing a 3-flowered spikelet (arrow).

FIGURE 5.Type locality (red star) of Paspalum prodigiosum Sánchez-Ken in Ario de Rosales, Michoacan, Mexico.